Water-repellent fibrous structures and process for obtaining same



Patented Dec. 5, 1950 WATER-REPELLENT FIBROUS STRUCTURES AND PROCESS FOROBTAINING SAME Kenneth L. Berry,

E. I. du

Bockcssin, DeL, minor to Pont de Nemours & Company, Wilmington, not, acorporation of Delaware No Drawing. Application February 5, 1947, SerialNo. 228,713

15 Claims. 1

This invention relates to a new water-repellent treatment for fibrousstructures and to the products so obtained.

Textiles have been rendered water-repellent by application of waxysubstances, such as hydrocarbons and long chain fatty acids orderivatives thereof, applied from solutions or dispersions. The majorproblems have been to choose the best materials, and to formulate andapply them so that the water-repellent finish is not removed by serviceand cleaning. In trying to solve these problems numerous treatments havebeen devised, but they generally have one or more 01' the followingshortcomings: l) the use of expensive or inflammable organic solvents isrequired, (2) the fibers are damaged by some of the chemicals orheat-treatments involved, (3) the treatment is applicable to only oneor, at best, a few fiber substances, (4) the process 01' application iscomplex, or (5) the water-repellent eiiect is lost or seriouslydiminished by laundering or dry cleaning.

This invention has as an object a simple and eilective process fortreating fibrous structures to make them water-repellent. A furtherobject is to provide water-repellent fibrous structures in which thefibers are essentially unchanged chemically, and in which the water-repllent effect is resistant to service. laundering, dry cleaning, andironing. Other objects will appear hereinafter.

The above objects are accomplished by impregnating fibrous structureswith an aqueous, colloidal dispersion of polytetrafiuorethylenecontaining as a surface active agent a small amount of a water-solublesalt of a polymeric amic acid,

and then baking the impregnated product until the amic acid salt hasbeen converted into a water-insoluble form.

The water-soluble salts used in the practice of this invention are, asdescribed more particularly hereinafter, an ammonium or basic amine saltoi a polymeric amic acid. These dispersing agents are particularlyvaluable for the present purpose. These salts, by reason of theirtransitory nature, do not contribute water-sensitivity to the filmobtained from the dispersion as do other dispersing agents.

It is also essential in accomplishing the objects of this invention thata colloidal dispersion of the polytetrafluoroethylene be used. Thesdispersions, as contrasted with suspensions of powdered polymer, areobtained by conducting the polymerization in aqueous systems which havelow ionic strength and in which the ms.-

terial polymerized consists essentially of tetrafiuoroethylene so thatthe homopolymer is obtained.

The polymeric amic acids, which are used in the form of their ammoniumor amine salts, are obtained by amidation of a polymeric polycarboxyiicacid anhydride with ammonia or a primary alkylamine such as ethyl,propyl, butyl and amylamines. Although the alkyl amines containing lessthan seven carbon atoms are preferred for this purpose, the longer chainaikyl amines up to 18 carbon atoms, for example, can be used.

The polymeric amic acids can be made either by suspending or dissolvingthe polymeric acid anhydride in a suitable organic solvent, addingammonia or a primary aikylamine with stirring, and then treating theresulting suspension either with ammonia, dilute aqueous ammoniumhydroxide or a water-soluble basic amine until the polymeric amic acidhas been converted to the ammonium or basic amine salt. The ammoniumsalt of the polymeric amic acid can be isolated by filtration or othermeans known to the art. The polymeric polycarboxylic acid anhydride isan lnterpolymer of a polymerizable organic compound containing anethylenic double bond as the sole carbon-towarbon unsaturation with anacid anhydride having the formula:

where R and R are hydrogen, alkyl, aryl, aralkyl or cycloallryl, forexample, methyl, ethyl, propyl, octyl, decyl, phenyl, tolyl, xylyl,benzyl and cyclohexyl. Methods for obtaining these copolymers are dscribed in U. S. Patents 2,047,398 and 2,378,629.

The mentioned ethylenically unsaturated organic compounds that areinterpolymerized with the acid anhydride include ethylene. propylene.butylene, isobutylene, styrene, indene, vinyl acetate. methyl acrylate,and methyl methacrylate. In these polymeric acid anhydrides the tworecurring non-oxo-carbonyl groups are attached directly to adjacentcarbon atoms of the polymeric chain.

In preparingthe polymeric amic acids it is preferred to react one moleof ammonia or a lower primary allrylamine with one mole of the polymericacid anhydride, assuming that the q i alent molecular weight of thepolymeric acid anhydride is that of the structural unit. The formationof the salt is effected. as has been noted previously, by treatment withammonia. ammonium hydroxide or water-soluble basic amine. These basicamines used have an ionination constant value greater than 1x10 whenmeasured at 25 0.. and are soluble to the extent of at least 5 parts per100 parts of water at 25 C.

A water soluble salt of a polymeric amic acid of the above describedtype which is readily prepared is that used in the subsequent examplesand consists of ammonium polystyrene/males.- mate. This sale wasobtained by the following procedure:

Finely divided styrene/maleic anhydride copolymer having a viscosity ofabout 6.2 centipoises at 25% solids in methyl ethyl ketone at 25' 0..was suspended in about times its weight of dry benzene and ammonia gaswas passed into the suspension during several hours, at which time anexcess of ammonia remained in the benzene. After standing for abouthours the product was removed by filtration and the ruidual benzene andexcess ammonia allowed to evaporate. The residual ammonium salt of thepolymeric styrene/maleamic acid was a finely divided, colorless solid,which dissolved readily in water. Such solutions at 10% solids and pH of8.0 have a viscosity of about centipolses at C.

The invention is illustrated by the following examples in which thepercentages are by weight. The water repellence rating mentioned isdetermined in the manner described in American Dyestuffs Reporter 30,6-14 (1941).

Example I Undyed, unsized cotton sateen is dipped three times in a 2.5percent colloidal poiytetrafluoroethylene dispersion containing 0.1percent ammonium polystyrene/maleamate as the surface active agent. Thecloth is baked for ten minutes at 230 F. after each dip. The clothbecomes successively more water repellent after each treatment. Thecloth is finally ironed and subiected to the spray rating test. It has awater repellence rating of 90, initially, and so after three severelaunderings.

Example H White. 9 as. cotton sateen is immersed in an aqueousdispersion containing 4 percent polytetrafluoroethylene and 0.1 percentammonium polystyrene/maleamate as a transitory dispersing agent. Thefabric is then passed through a wringer, dried and baked five minutes at250 F. to convert the dispersing agent to its insoluble form. The fabricthereby is rendered remarkably water-repellent; furthermore. the waterrepellenc remains after severe laundering and dry cleaning treatments.

Example H! White 9 oz. cotton sateen is immersed in an aqueousdispersion containing 5 percent polytetrafiuoroethyl ne, 0.1 percentammonium polystyrene/maleamate. and 1 percent of dimethylol p-cresol.The fabric is passed through a wringer, then dried and baked fiveminutes at 85 1". to convert the di-methylol compound to a resin. Theresultant finish ail'ords excellent water-repellence which is unchangedafter three severe launderings and still serviceable for essentially thelife of the fabric.

4 Sample [7 A nylon fabric is treated as in Example In with a 5 percentpolytetrafiuoroethylene dispersion crntaining 0.1 percent ammoniumpolystyrene maieamste and 1 percenthexamethyiene-bis-(cycloethylene-urea). After curing by baking 5 minutesat 800' I". a desirable waterrepellent finish is obtained.

Example V White, a olrcotton sateen is treated as in ex ample II! with a2.5 percent polytetrailuoroethylene dispersion containing 1.3 percentmethylene-bis-(stearamide) and 0.8 percent ammoniumpolystyrene/maieamate. After curing 5 minutes at 850 It, the fabric anexcellent, durable water repellent finish.

Example W Cotton sateen is treated as in Example V. the dispersioncontaining as a fourth component 0.5 percent of di-methylol p-cresol.The finish, after curing 5 minutes at 350 F.. is water repellent anddurable for the life of the fabric.

Although it is not necessary. it is sometimes desirable to incorporatein the treating dispersions auxiliary materals such as pigments. resins.and other modifiers to obtain optimum results. Instead of dipping. thesedispersions can be applied to the fibrous structures by spraying,painting and flowing.

The aqueous dispersion of polyte rafiuoroethylene used in the exampleswas obtained by the following procedure:

A pressure vessel fitted with a gas inlet tube was filled approximatelytwo-thirdsjull with a 0.1% aqueous solution of disuccinic acid peroxide.The vessel was then evacuated and heated to C. Tetrafiuoroethylene wasled into the vessel at a. pressure of 850 p. s. i. and the latteragitated continuously for about 3 hours. At the end of this time therewas obtained a colloidal dispersion of polytetrafluoroethylenecontaining 4% of polvtetrafiuoroethylene.

The particles of polytetraiiuoroethylene in the dis ersion are ofcolloidal size and are frequently rod-shaped. The smaller dimension isof the order of 0.1 micron while the larger dimension rangesapproximately from 0.1 to 0.8 micron. The dispersions, as prepared, areunstable in that the solid phase is readily coagulated by flotationagitation, by small concentrations of ions. or watermiseible organicliquids. It is for this reason that the dispersions are stabilized byaddition of a water-soluble ammonium or amine salt of a. polymeric amicacid. which because of its transitory nature does not contributewater-sensitivity to the dried film. Since the polymeric amic acids arewater-insoluble. it is necessary that the pH of the p0tetrafluoroethylene dispersions be raised above a pH of 5 and preferablyabove a pH of '1 by addition of ammonia prior to addition of thewatersoluble salt of the polymeric amic acid.

The best results are obtained with dispersions having anolvtetrailuoroethylene concentration pf from 3% to 8% by weight.although concentration of from 2% to 40% can be used. The preferredsolids concentration is determined by how much polymer is desired in thefabric and how many impregnations can be employed to deposit this amountof polymer. For maximum economy it is desirable to employ only one imprenation and to deposit the minimum amount of polymer necessary to get thedesired water-repellent effect.

avenue:

Solids concentrations can be reduced by addin water to the dispersions.Dispersions may be concentrated when necessary by such known methods asevaporation. ultraflltration, electrodecantation. or reversibleflocculation.

Examples of other ammonium or amine salts of the polymeric amic acidthat can be used in place of the salt mentioned in the examples arethose of polymeric N-methyl styrene/maleamic acid. polymeric N-ethylstyrene/maleamic acid, polymeric N-propyl ethylene/maieamic acid."polymeric N-cyclohexyl propylene/maleamic acid, polymeric N-isopropylstyrene/maleamic acid, polymeric N-phenyl styrene/maieamic acid and thelike. Such polymeric amic acids of different molecular weight andsolution viscosity characteristics may be used. In general. however.prodnets of low viscosity characteristics are preferred, for example,products having a viscosity of less than 200 centipoises at 10% solidsin aqueous solution at 25 C. and at a pH of 7 to 8. Further details withregard to the preparation of these water-soluble amic acid salts arecontained in applicatlon Serial No. 663,642, filed April 19, 1946, by M.E. Cupery now U. S. Patent No. 290,677. The polytetrafluorcethylenedispersions used in the practice of the present invention contain theamic acid salt in amounts of from 0.1 to 10%. and preferably from 2% to5% of the weight of the polytetrafluoroethylene in the dispersion.

For application of the dispersions to fibrous structures. e. g.,fabrics, simple dipping of the fabric in the dispersion is preferred.The fabric is then wrung to remove excess dispersion and allowed to dry.At this stage the treated fabric has excellent water-repellency and thetreatment has surprising resistance to dry cleaning and laundering. Animprovement in water-repellency and resistance to dry cleaning andlaundering is obtained by baking the coating at temperatures above 212'F. for about 5 to minutes; this baking treatment converts the polymericamic acid salt dispersing agent to a. water-insoluble form. the saltprobably being converted to an imide by the heating. The bakingtemperature must be below the decomposition temperature of the fibrousmaterial used. In the case of fibers of organic composition, such ascellulose, wood, nylon. viscose rayon, linen. vinyl resins. andcellulose esters, the preferred temperatures are in the range of from225 F. to 350 F. These temperatures do not cause fusion of thepolytetraiiuoroethylene and it is surprising that a permanentwater-repellent effect is developed without fusion of the polymer. Whenheat-resistant inorganic fibers. such as glass. asbestos and certainmetals are used, baking temperatures of up to or above 621 F'. (thetransition point of the polytetrafluoroethylene). but below thetemperature at which the fiber disintegrates can be employed. In thiscase the polytetrafluoroethylene is sintered and the permanency of thewater-repellent eil'ect conferred is essentially absolute.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof. it is to beunderstood that the invention is not limited to the specific embodimentsthereof except as defined in the appended claims.

I claim:

l. A composition of matter which comprises a colloidal aqueousdispersion of polytetraiiuoroethylene containing from 2% to 40% ofpolytetrailuoroethylene and from 0.1% to 10% by weight of thepolytetrafluoroethylene of a salt of the class consistin of ammonium andwatersoluble basic amine salts of an N-monoalkyl substituted polymericamic acid of an interpolymer of a polymerizable organic compoundcontaining an ethylenic double bond as the sole aliphaticcarbon-to-carbon unsaturation with a butenedioic acid anhydrlde. therecurring two non-oxo carbonyl groups in said polymeric amic acid bein!attached directly to adiacent carbon atoms of the polymeric chain whichcontains structural units in which the amide nitrogen atom has attachedthereto hydrogen and a long-chain monoalkyi substituent of at leastseven carbon atoms. the basic amines of said salts being those having anlon'zation constant Value greater than 1 x 10- when measured at 25 C.

2. The composition defined in claim 1 in which said salt is the ammoniumsalt of said polymeric amic acid.

3. The composition set forth in claim 2 in which said polymeric amicacid is polymeric styrene/maleamic acid.

4. The composition defined in claim 1 in which said salt is a basicamine salt of said polymeric amic acd.

5. The composition set forth in claim 4 in which said polymeric amicacid is polymeric styrene/maleamic acid.

6. A process for obta ning a water-repellent fibrous structure whichcomprises impregnating said structure with an aqueous colloidaldispersion containing from 2% to 40% by weight of thepolytetrafluoroethylene and from 0.1% to 10% by weight of thepolytetrafluoroethylene of a salt of the class consisting of ammoniumand water-soiuble bas'c amine salts of an N-monoalkyl substitutedpolymeric amic acid of an interpolymer of a polymerizable organiccompound containing an ethylenic double bond as the sole aliphaticcarbonto-carbon unsaturation with a butenedioic acid anhydride, therecurring two non-oxo carbonyl groups in said polymeric amic acid beingattached directly to adjacent carbon atoms of the polymeric chain whichcontains structural units in which the amide nitrogen atom has attachedthereto hydrogen and a long-chain monoalkyi substituent of at leastseven carbon atoms, the basic amines of said salts being those having anionization constant value greater than 1X 10-" when measured at 25" C.,and halt ng the impregnated fibrous structure at a temperature above 212F. and below the decomposition temperature of the fibrous structure.

'7. The process set forth in claim 6 in which said salt is the ammoniumsalt of polymeric styrene/maleamic acid.

8. The process set forth in claim "i in which said polymeric amic acidis polymeric styrene/maleamic acid.

9. The process set forth in claim 6 in which sa'd salt is a basic aminesalt of said polymeric amic acid.

10. The process set forth in claim 6 in which said polymeric amic acidis polymeric styrene/maleamic acid.

11. A fabric impregnated with polytetraiiuoroethylene and with the heatconversion product of a salt of the class consisting of ammonium andwater-soluble basic amine salts of an N- monoallcyl substitutedpolymeric amic acid of an interpolymer of a polymerizable organiccompound conta'ning an ethylenic double bond as the sole aliphaticcarbon-to-carbon unsaturation with a butenedioic acid anhydride, therecurring two non-oxo carbonyl groups in said polymeric amic acid beinaattached directly to adjacent carbon atoms of the polymeric chain whichcontains structural units in which the amide nitroaen atom has attachedthereto hydrogen and a long-chain monoalkyl substituent of at leastseven carbon atoms, the basic amines of said salts being those havinc anionization constant value greater than 1x10 when meas- .ured at 25 C. inamount of from 0.1% to 10% by weight of the polytetrafluoroethylene.

12. The imprea'nated fabric defined in claim 11 in which said heatconversion product is that of the ammonium salt of said polymeric amicacid.

13. The impregnated fabric defined in claim 12 in which said polymericamic acid is polymeric styrene/maleamic acid.

it. The impregnated fabric deiined in claim 11 in which said heat 8conversion product in that 5 styrene/maleamic acid.

KENNETH L. BERRY.

REFERENCES CITED The following references are of record in the 10 fileof this patent:

UNITED STATES PA'I'EN'IB Number Name Date Fikenstcher Oct. 9, 1934Alithan Apr. 20, 1948 Alderson Oct. 12, 1948 Cupery Dec. 14, 1948 CuperyFeb. 7, i950

1. A COMPOSITION OF MATTER WHICH COMPRISES A COLLOIDAL AQUEOUSDISPERSION OF POLYETRAFLUOROETHYLENE CONTAINING FROM 2% TO 40% OFPOLYTETRAFLUOROTHYLENE AND FROM 0.1% TO 10% BY WEIGHT OF THEPOLYTETRAFLUOROETHYLENE OF A SALT OF THE CLASS CONSISTING OF AMMONIUMAND WATERSOLUBLE BASIC AMINE SALTS OF AN N-MONOALKYL SUBSTITUTEDPOLYMERIC AMIC ACID OF AN INTERPOLYMER OF A POLYERMIZABLE ORGANICCOMPOUND CONTAINING AN ETHYLENIC DOUBLE BOND AS THE SOLE ALIPHATICCARBON-TO-CARBON UNSATURATION WITH A BUTENEDIOIC ACID ANHYDRIDE, THERECURRING TWO NON-OXO CARBONYL GROUPS IN SAID POLYMERIC AMIC ACID BEINGATTAHCED DIRECTLY TO ADJACENT CARBON ATOMS OF THE POLYMERIC CHAIN WHICHCONTAINS STRUCTURAL UNITS IN WHICH THE AMIDE NITROGEN ATOM HAS ATTACHEDTHERETO HYDROGEN AND A LONG-CHAIN MONOALKYL SUBSTITUENT OF AT LEASTSEVEN CARBON ATOMS, THE BASIC AMINES OF SAID SALTS BEING THOSE HAVING ANINOZATION CONSTANT VALUE GREATER THAN 1X10-6 WHEN MEASURED AT 25*C.